This invention relates to an apparatus for hardening a mold article such as sand molds or sand cores of sand and a binder hardenable by a catalyst gas in molding boxes, in which a reduced pressure source evacuates the molding box to a predetermined pressure less than atmospheric pressure, the catalyst gas is then briefly delivered to the molding box with a slight increase in the absolute pressure, after which the molding box is filled with fresh air and evacuated by means of the reduced pressure source.
Sand molds or sand cores for foundry purposes, which consist of a mixture of sand and a binder, are hardened by means of a catalyst gas which is forced or sucked through the sand molds or sand cores. The catalyst gas initiates a chemical reaction in the binder, only a minimal proportion of the catalyst gas passed through the sand molds or sand cores being consumed. Accordingly, the quantity of catalyst gas issuing from the sand molds or sand cores substantially corresponds to the quantity of catalyst gas delivered to the sand molds.
The catalyst gases used for hardening the sand mold are more or less toxic and dangerous so far as the human organism is concerned. Accordingly, the catalyst gases issuing from the sand molds cannot be let off into the surrounding atmosphere and workshops if physiological damage to personnel is to be avoided.